Viscose process



May 24, 1960 R. L. MITCHELL ET A 2,937,922

vxscoss PROCESS Filed March 24. 1954 United Sftates Patent 2,937,922 VISCOSE PROCESS Reid Logan Mitchell, James Wesley Berry, and William Hughes Wadman, Shelton, Wash., assignors to Rayonier Incorporated, Shelton, Wash., a corporation of Dela- Ware Filed Mar. 24, 1954, Ser. No. 418,384

5 Claims. (CI. 18-54) This invention relates to the viscose process, and has for its object the provision of improvements in the viscose process. The improved products produced by the invention are characterized mainly by greatly increased strength and a highly ordered orientation of the crystalline elements, and by low swelling properties. While the invention is applicable generally to the coagulation and regeneration of variously shaped products which are stretched during regeneration, it is most advantageously applicable to the production of filaments for use in textiles and tire cord.

Viscose rayon filaments of general utility have many shortcomings as compared with other textile materials, manifested by low strength, particularly when wet, and high reswelling, both being attributable to a low degree of order of the regenerated structure. However, increased tensile strength in tire cord type rayon has been attained largely by prolonging the period of regeneration, permitting more time for the cellulose crystal structure to form while at the same time imposing stress to further uniaxially orient the crystalline elements being developed. Various expediencies have been resorted to to balance the conditions of coagulation and regeneration favorable to the development and orientation of crystalline elements to produce filaments having a high degree of order, high strength and low swelling properties. It has been proposed to prolong the regeneration period and keep the filaments as long as possible in a metastable, stretchable state while at the same time applying maximum stress to give a high degreeof orienting stretch.

This invention provides an improved process in which the filaments receive a substantially uniform state of decomposition or regeneration throughout their cross section. The process effects such a control over the conditions that the inner portions of the filaments are almost as accessible or responsive as the outer portions to the regenerating reagents, the entire cross section of the filaments being maintained in an intermediate state of regeneration with high stretchability for a sufficient period to permit a relatively high degree of stretch.

In accordance with one improved process of the invention, it is important to use a viscose containing cellulose having a relatively uniform chain length at a given level within the range 300 to 800 DP '(degree of polymerization) and to spinthe viscose into filaments under special chemical and physical conditions.

It is advantageous in one aspect of the invention to form viscose having a salt index of from 6 to 20 and to spin the viscose into a spin bath having from 6% to 12% zinc sulfate (ZnSO or equivalent metal sulfate, preferably containing from 9% to 10% of sulfuric acid I (H 804), at a temperature of from 45 to 70C., and

so that the entire cross sections of the filaments, the inner portions being substantially as accessible as the outer portions, are maintained for a relatively long period in an intermediate state of regeneration during which time the filaments are susceptible to high stretchability. Modifiers effective in the process of the invention for incorporation 'in the viscose include nonionic agents, such as the block copolymers of polyethylene oxide and polypropylene oxide, for example those known as Pluronics. The block copolymers sold under the name Pluronics are produced by the Wyandotte Chemical Corporation. Particular block copolymers known as Pluronics L62, L64, L61, L44, and F68 give effective results, L64 being particularly effective. Among other agents which show some regeneration retarding action are the simple polyethylene oxides, polypropylene oxides and compounds of alkylphenolethylene oxide condensation products. These agents may be added to the viscose alone or in combination, or in combinationwith amines, for example di- .methylamine or cyclohexylamine, or with dimethylformamide. These non-ionic agents are carried along into the spin bath where they accumulate and, among other things, suppress the formation of craters on the spinnerets. It has been common practice to use such anti-cratering agents in spin baths to prevent crater formation but around 0.005% by weight based on the viscose has been suflicient for this purpose. In this process, the surprising results in the control of regeneration require, say, from 0.1% to 1.0% by weight based on the viscose added in the viscose itself. With regard to the block copolymers, there is a sufiicient carryover to the spin bath to build up a substantial equilibrium value which modifies the reaction in which the cellulose xanthate is decomposed to yield cellulose. The block copolymers in particular, when used in the amounts of the invention, are in some instances thrown out of solution and form a floating layer on the surface of the spin bath. It may be that there is a sufiicient amount of the block copolymer in viscose and the spin bath to coat the freshly extruded filaments and effect a retardation of the penetration of the acid while permitting entry of the zinc, thereby permitting more extensive stretch. When using block copolymers, it is preferred to allow the spin bath to reach equilibrium conditions before attempting to spin high tenacity filaments.

While the resulting action is not fully understood at this time, it appears that these non-ionic agents not only remove resin particles from the surface but also from the interior of the filaments. They make it possible in conjunction with high concentrations of zinc sulfate or equivalent metal sulfate in the spin bath to maintain with good continuity extremely high orienting stretch. The spinning conditions of the invention result in a relatively long period of regeneration during which time the filaments are stretched so as to achieve a high degree of order, high strength and low swelling properties. In order to effect a proper control over the decomposition and regeneration of the filaments, it is preferred to provide a long bath travel before gathering the filaments, for example, a distance of around 15 to 60 inches or more, depending on spinning speed, from the spinneret to the gathering hook. A total bath travel of around 150 to 250 inches generally gives satisfactory results.

Suitable arrangements may be made to change the stretch pattern, effect earlier stretch and increased tension by the use of large tension wheels. Suitable long contact with the spin bath while undergoing high stretch may be accomplished by use of a modified stretching setup on the Kuljian machine or other pot, bobbin or continuous type spinning frame.

The viscose may be modified further by adding directly to the viscose suitable inorganic or organic zinc compounds to aid in controlling the uniformity of regeneration. It appears that the process of the invention causes a more effective and complete penetration of the zinc of the spin bath into the center of the filaments. This action may be further aided by the incorporation of suitable zinc compound into the viscose before spinning.

In another aspect of the invention, dimethylformamide or dimethylamine is incorporated in the viscose or in the spin bath to control the regeneration of the filaments. It appears that the addition of dimethylformamide to the viscose results in decomposition forming dimethylamine. Dimethylamine may, accordingly, be present in the spin bath either by direct addition or by adding dimethylformamide to the viscose or the spin bath. It appears that dimethylamine has a greening or regeneration retarding action on the filaments and may also function as a gas solvent to suppress the formation of gas as such within the green filaments. The dirnethylformamide or dimethyl amine may be added to the viscose in any suitable amounts, for example, in amounts up to about 1%, with or without the addition of Pluronics.

Still other aspects of spin bath treatment may comprise the incorporation in the spin bath of other amides the combination of Plnronics and amines, and the combination of Pluronics, amines and dimethylformamicle.

In another embodiment of the invention, one or more of the agents, such as Pluronics, dimethylformamide or dimethylamine, are incorporated in the viscose and the viscose thus treated is spun into any suitable spin bath, such as one containing a relatively high content of zinc such as zinc sulfate or equivalent metal sulfate such as iron or manganese.

In accordance with a process of the invention, the filaments are preferably given a relatively long travel through the spin bath adjusted to spinning speed and during regeneration the filaments are subjected to an exceptional amount of stretch, varying, say, from 70% to around 200%, and even up to 1000%. The resulting filaments, when given the common differential dye test to distinguish skin from core, appear to be all-skin," and have tensile strengths upwards of 3.5 g. per denier while exhibiting exceptional resistance to fatigue.

In carrying out the process of the invention, a viscose may be spun having a DP level of from 300 to 800 and relatively uniform chain length prepared from celluloses such as sulfite wood cellulose, for example, Rayocord X, prehydrolyzed kraft, cotton linters, resin free pulp, high DP pulp of uniform chain length, and preoxidized pulp of low DP and uniform chain length.

The viscose solution may comprise cellulose and caustic soda in any suitable proportions, the cellulose varying from 4% to 13% and the caustic soda varying from 5% to 13%. Particular viscose solutions may comprise:

7.5% cellulose and 6.5% caustic soda 8.0% cellulose and 7.0% caustic soda 9.0% cellulose and 8.0% caustic soda 10.0% cellulose and 12.0% caustic soda 10.0% cellulose and 9.0% caustic soda 13.0% cellulose and 13.0% caustic soda 5.0% cellulose and 6.0% caustic soda 6.5 cellulose and 6.5 caustic soda The invention is advantageously applicable to the conventional viscose compositions comprising around 7.5% cellulose and 6.5% caustic soda.

To obtain viscose with a spinning index of about 15, the

usual practice is to xanthate the alkali cellulose with about 45% of carbon bisulficle. Advantageously, one may xanthate with the normal 34% carbon bisulfide and then add to the mixed viscose the additional carbon bisulfid'e to bring it to the desired high sodium chloride index. This results in savings of carbon bisulfide, reduced amounts of by-products, and more convenient xanthation. Also, low mixing temperatures, such as 12 C., may be advantageously used to maintain sodium chloride index.

In carrying out a more or less complete operation in one embodiment of the invention, a block copolymer of polyethylene oxide and polypropylene oxide represented by the formula in which x has an average value of about 16 and y has an average value of about 28 is mixed into the viscose spinning solution in amounts varying from 0.1% to 1.0% by weight based on the viscose. The compound Pluronic L-64 is of this type and is very effective for carrying out this aspect of the invention. -It appears that the use of a block copolymer in the viscose, in addition to the dispersion of resins as aforementioned, also retards regeneration and alleviates the formation of gas bubbles in the green viscose during decomposition. Regardless of the action of the block copolymer, its use facilitates the use of relatively high concentrations of zinc sulfate in the spin bath and results in cumulatively retarding the rate of regeneration whereby the filaments may be stretched more extensively during their transformation from the green state to a highly oriented crystalline structure. The action of the block copolymer may be further accentuated by adding dimethylformarnide or dimethylamine to the viscose or to the spin bath in amounts of about 0.1% or more. The dimethylformamide and dimethylamine act as greening agents and appear also to act as gas solvents or in some manner to control the conditions which inhibit the formation of gas bubbles in the filaments. When the dimethylformamide or dimethylamine is used in a spin bath for the spinning of viscose containing a block copolymer, the production of all-skin filaments, of superior rounded cross sectional shape, free of bubbles, of high tensile strength and improved fatigue properties is facilitated.

The term all-skin comes from a dyeing technique now in common use whereby thin filament cross sections are processed with certain dyes which act selectively with respect to ordered and disordered cellulose. Ordinary textile rayon cross-dyed by this method shows a thin outer skin of highly ordered cellulose dyed in one color surrounding a low-ordered core of much larger area dyed in another color. Regular tire cord rayon dyed in the same manner shows a much thicker skin of high order surrounding a smaller core of low order.

In still another embodiment of the invention, paranitrosodimethylanaline or hexamethylenediamine may be added to the viscose to retard regeneration. While the solubility of this compound is low, it exerts strong retarding action, and small quantities of the order of 0.1% or less based on the viscose are effective.

Figs. 1, 2 and 3 of the accompanying drawings show the cross sections of the filaments which are dyed as described and under a magnification of 2200, the dark portions representing the highly ordered and oriented skin portions.

Fig. 1 illustrates the cross sections of ordinary textile rayon filaments;

Fig. 2 illustrates ordinary tire cord rayon filaments;

Fig. 3 illustrates"all-skin rayon filaments of the invention.

The following examples illustrate viscose spinning operations carried out in accordance with the process of the invention:

Example 1 A viscose of 7.5 cellulose content, 6.5 sodium hydroxide and 0.1% added dimethylamine was spun at a sodium chloride index of 16.0 into a spin bath of 9.0% H 30 18% Na SO 9% ZnSO 0.1% lauryl pyridinium chloride and 1.0% added dimethylformamide at 52 C. The extruded filaments (980 to yield a total finish denier of 1640) were led t rough a system of vaned rollers for a bath travel of 180 inches, stretched more than 100% in the spin bath, withdrawn onto a godet under a tension of 1000 grams, treated with hot water at 80 C., stretched an additional 30% under a tension of 1600 grams, relaxed 5% and wound on a bobbin at 55 meters per minute.

Filaments of this yarn were more than 90% skin and had a conditioned (75 F., 60% R.H.) tendency of 4.8 grams/denier and conditioned elongation of 9.5%. A 2 ply, 11 x 11 construction cord made therefrom had a denier of 3700, conditioned tenacity of 3.50 with fatigue life of 465.

When dimethylformamide was used in the viscose in place of dimethylamine or dimethylamine used in the spin bath instead of dimethylformamide, the results were substantially the same.

Example 2 A viscose of 5% cellulose and 5% sodium hydroxide containing 0.1% added dimethylamine was spun at 16.0 NaCl index into a spin bath having 9.0% H 80 17% Na SO 9.5% ZnSO and 1.0% added dimethylamine maintained at 50 C. under conditions subjecting a 1650 denier thread to 150% total stretch with 1050 grams/ denier primary tension and 1750 grams/ denier secondary tension.

The above viscose of low cellulose concentration with only slightly high spinning viscosity contained cellulose of about 800 DP as compared with a normal 7.5-6.5 viscose containing cellulose of 400 DP.

Yarn, and resultant cord, prepared in the above manner from 800 DP cellulose had substantially higher tenacity and fatigue life than yarn and cord prepared in similar manner from 400 DP cellulose.

In ordinary spinning operation, without added regeneration retardants, this is not the case because the low cellulose viscose yields a yarn of low density and spongy texture for which strength advantages of the higher DP has been more than canceled-out by the cheesy structure of the filaments.

With added regeneration retardants, however, filaments spun from low concentration viscose have time to become dehydrated, shrunken and consolidated in structure by the astringent action of the bath before regeneration and structural setting takes place.

Other low cellulose viscose compositions are useful in giving high DP in the yarn, e.g., 6% cellulose with 6% sodium hydroxide or 5% cellulose with 6% sodium hydroxide.

High DP in the yarn may also be obtained by spinning normal viscose compositions such as 7-6 or 7.5-6.5 at high viscosity in the range of 100-1000 seconds as compared with a normal of 35 seconds. However, inconvenience experienced in filtering and spinning such thick viscose dispersions is considerable.

What is claimed is:

1. In the viscose process the improvement which comprises forming a viscose solution containing about 5% each of the cellulose and sodium hydroxide, said cellulose having a degree of polymerization of about 800, spinning the viscose into an acid spin bath containing from about 0.1% to 1.0% of dimethylamine, and stretching the filaments in excess of while in contact with acid spin bath solution producing all-skin filaments.

2. In the viscose process the improvement which comprises forming a viscose spinning solution having a salt index of from 6 to 20 containing cellulose of relatively uniform chain length, the degree of polymerization of which is from 300 to 800, incorporating in the viscose from about 0.1% to 1.0% of dimethylamine as a regeneration retardant, spinning the viscose into a regenerating acid spin bath, keeping the filaments in contact with spin bath solution while stretching them at least 70% and until regeneration has proceeded to the formation of all-skin filaments.

3. In the process of claim 2, stretching the filaments while traveling a distance up to 250 inches in contact with spin bath solution.

4. In the process of claim 2, adding zinc sulfate to the viscose.

5. In the process of claim 2, adding to the viscose hexamethylenediamine.

References Cited in the file of this patent UNITED STATES PATENTS 2,225,604 Lubs Dec. 17, 1940 2,297,746 Charch Oct. 6, 1942 2,442,331 Cresswell June 1, 1948 2,535,044 COX Dec. 26, 1950 2,535,045 Cox Dec. 26, 1950 2,586,796 Drisch et a1 Feb. 26, 1952 2,592,355 Tachikawa Apr. 8, 1952 2,607,955 Drisch et al Aug. 26, 1952 

1. IN THE VISCOSE PROCESS THE IMPROVEMENT WHICH COMPRISES FORMING A VISCOSE SOLUTION CONTAINING ABOUT 5% EACH OF THE CELLULOSE AND SODIUM HYDROXIDE, SAID CELLULOSE HAVING A DEGREE OF POLYMERIZATION OF ABOUT 800, SPINNING THE VISCOSE INTO AN ACID SPIN BATH CONTAINING FROM ABOUT 0.1% TO 1.0% OF DIMETHYLAMINE, AND STRETCHING THE FILAMENTS IN EXCESS OF 70% WHILE IN CONTACT WITH ACID SPIN BATH PRODUCING ALL-SKIN FILAMENTS. 